bug#9366: Display geometry change hook

[Eli Zaretskii]

> Cc: david@harpegolden.net, 9366@debbugs.gnu.org
> From: martin rudalics <rudalics@gmx.at>
> Date: Sun, 20 Sep 2020 10:14:34 +0200
> 
>  > Do we really have to do this on such a low level?  Why cannot we call
>  > such a hook from change_frame_size, which would allow us to do that in
>  > platform-independent manner?
>  >
>  > Martin, am I missing something here?
> 
> Would change_frame_size be aware of such a geometry change?  IIUC
> the original request
> 
> https://lists.gnu.org/archive/html/emacs-devel/2011-08/msg00544.html
> 
> Edward would really just want a completely separate hook that reports to
> Emacs the identity of the changed display and maybe its new geometry and
> is only called in those, IMO very rare, occasions.  Or what am I missing
> here?

So this is only about switching to a different display?  And you are
saying that Emacs in general doesn't know about such display changes?

Would it work to test the display geometry from focus-in-hook?  Or
from a timer?